1987 300SDL engine cooling fan removal and tensioner repair
 

Hi All, First post to this board, I own 3 MBZs and do work on them for friends. I am a member of the Turbo Diesel Register (Cummins Diesel powered Dodge forum). All of my cars are diesels with the exception of a restored '55 VW Bug. I am looking forward to participating on this site and I bring 35 years of mechanical experience and 23 years of diesel experience.

Question: I'm working on a '87 300 SDL and the accy belt tensioner is riding crooked. What is the secret to rebuilding this?
Also, how does the cooling fan clutch remove from the water pump? Thanks,Chris

Do a search on tensioner... I think you'll be better off with a new one. to remove the fan clutch insert a L shape 5 mm allen into the little hole at the back of the spindle and held it against the ridge on the water pump's 'neck' to stop it from spinning. turn the 10 mm allen bolt in the center of the fan clutch CC.

Thanks for the info!! Chris

yup, replacement is generally what is done - I think
 

I replaced my crooked tensioner a few weeks ago.

It was pretty easy. You may also want a new pulley and maybe a new tensioner shock/damper.

With all of those pieces, you should be finished with that part of the car for several tens of kmiles.

later

Chris,

You can't fix the tensioner lever arm, you replace it. It's about $50 new. And do it ASAP, once it cocks far enough it can tear up the timing case which makes for a large, very expen$ive job. The tensioner arm is a known weakness of these engines. Expect to replace it every 50-100kmi, possibly less (I had one fail - leaking grease - after ~20k.) The shock has an incredibly short life span as well, sometimes as low as 10-20kmi. If leaking, or if the bushings are torn up, replace it. Rumor is the OE dealer shock lasts longer than the Bilstein or Febi aftermarket ones.

You may need a new idler pulley, depends on condition when you remove it. You WILL need both new plastic caps, but they're only about $1 each. There are special tools that make clutch removal easier (and much faster) but they're not required. Check the serp belt too while you're in there, if the ribbed area has cracks might as well change that too. When installing the new arm, either use blue LocTite or a non-hardening sealer, as the bolt hole goes into the oily timing chain cavity. MB specs "Omnifit Orange" but I've never bothered to buy that stuff. Just do NOT use red LocTite as some folks say! When all done you'll be set for a long time.

Last tip: The vacuum pumps are also a known problem on these engines. The original design was flawed. If your car has the original pump, replace it NOW before the bearing fails & dumps innards inside the crankcase (worst case it gets in the timing chain, destroying the engine). This is not a hard job but a new pump is $175 last time I checked at ***************...


Good luck,

gsxr, Thanks for the VERY important info on the 6cyl. I am very familiar with the 5cyl and the 4 cyl diesel but learning all the time on the 6 cyl. I will talk to the owner of the car about the vac pump. The car has 192,000 mi, runs well. I am also trying to find out why it studders at cold start. I have changed ALL fuel lines and return lines, both fuel filters, and pulled the glow plug harness at the relay and checked the glow plugs with an ohm meter. All read good. I did notice that the previous owner had replaced only 3 injectors..Cyl4,5,6. The compression seems good, it has very minimal blow-by when you pull the oil cap off at hot idle. Any other ideas?

I can already tell this is a great site!! Thanks, Chris

Chris,

No problem, happy to help out. Since you are new to the OM603 engine, I'll mention one last thing. Do not EVER let it overheat. The original aluminum head design was flawed and will crack fairly easily (compared to the old iron head, which was almost indestructible). MB redesigned the head 3 times and the gasket 5 times. Normal operating temps are 80-100C under almost all conditions. Under blistering heat with the A/C on climbing a mountain, you may see 105-110C but that's it. Anything more, or if you see those temps when it's cool outside, and your cooling system needs attention. The fan clutch tends to die after ~10 years and the radiators plug internally if you don't use MB antifreeze and change it every 2-3 years. If you have the evil "green" stuff in there, get rid of it ASAP. The MB antifreeze is a special formula for iron & aluminum components, unlike ANY other a-f on the market. It's only ~$10/gallon so $10 per 3 years isn't bad insurance. If the fan has plastic blades, the clutch is probably recent. If not, watch the temp gauge! :)

Now, about the cold start. If it's just the first 5-20 seconds after startup and then it's OK, try letting the glow plugs stay on longer before cranking... let them heat up 5-15 seconds more AFTER the dash light goes out. Then start up. If that has NO effect, either you have carbon buildup around some of the glow plugs (reducing their efficitve heating ability, regardless of resistance measurements) OR you may have a fuel injector problem. Glow plugs should measure 0.6 ohms each. Driving the car HARD is good for the engine and keeps carbon cleared out, so "drive it like you stole it" as much as possible - trips to the redline are GOOD for it! Really! I find it odd that only 3 injectors were replaced. Worst case, you pull all 6 and have them pop tested at a diesel shop & checked for leaking, good pattern, etc. The compression should be good, these engines rarely have worn bottom ends if maintained well (regular oil changes every 5k with dino, 10k with synthetic, more often if city driven).

Finally, yep, this is a VERY good Mercedes tech board. The other resource I highly recommend is the MBZ.org diesel email list. The traffic is fairly high so sign up for the digest version. There are several folks who have small fleets of OM60x-engined MB's and the collective knowledge is fantastic. Also play with the "search" function on this forum, there is a TON of information in the archives, you just need to find it!

:D

Good luck,

Dave, I had heard of the aluminum head problems on the 6 cyl. My opinion is that aluminum heads on diesels are a no no. I tell all of my clients to NEVER let a Diesel overheat...especially ones with alum. heads. Thanks for the info on the studder at startup. I have left the glows on longer and it starts better. The owner DOES drive it like He stole it... I will caution him though to wait untill it is up to temp before standing on it. Chris

On the aluminum head, once Mercedes got it right (after 4 tries) the resulting head is pretty crack-proof. I have not heard of a SINGLE redesigned head (most 1990-up) failing - yet. :)

That is good to know. I doubt that the head on this guys '87 has been changed. On the Dodge/Cummins site, I heard that the GM Duramax (Isuzu diesel V8) has aluminum heads and they have had problems also. Chris

hey guys. i am having trouble with this particular step. i want to remove the fan but i don't see any "holes" on the fan spindle to stick a 5mm allen. where exactly is the hole?

i looked at a picture of the spindle assembly but the picture is too small to determine where the allen goes. your help is appreciated. thanks!

603 engine
 

I just did my '87 300D which has the same engine, IMHO. There is no hole to use to stop the pulley from rotating. I was able to use the serpentine belt itself to hold the pulley; there's also a factory tool for the purpose. Anyway, I used an 8 mm Allen wrench with a short length of 1/2 inch pipe for added leverage to remove the bolt holding the fan and clutch to the pulley. Unclip the fan shroud and move it back over the fan to get yourself a little room in front of the fan -- it's tight. Some folks have reported better access by cutting the short end of the Allen wrench even shorter.

Once the fan and shroud are off, loosen the tensioner and remove the serpentine belt from the idler pulley. The idler is held to the timing cover with -- I think -- a 12 mm Allen bolt.

The fan and clutch can be upgraded to the plastic fan and new clutch that came with the 606 engine. My fan was not causing problems but I upgraded anyway -- the plastic fan saves several pounds of rotational mass.

Allowing the engine to glow a little longer will help it to start and run more easily. You can also modify the glow plug relay to add afterglow (there's a thread on the subject in this forum) or install a later relay with afterglow built in.

Jeremy

i tried that with the belt on. still no joy. any other ideas?

Make a wedge out of a piece of wood and wedge the belt at the power steering pulley so it cannot rotate.

When you get the wrench in position on the cap screw..........use an extension on the socket wrench so that it comes up above the radiator (a piece of 1/2" pipe works well). Then, give the pipe a hit with a sledge hammer to break the screw loose.

Try loosening the tensioner and mostly removing the serpentine belt. Leave the belt wrapped around the water pump pulley and clamp the belt to itself with a vice-grip pliers. That will allow the belt to act as a strap wrench. With that, you should be able to hold the pulley so that it won't turn while you unfasten (turn counter-clockwise) the bolt in the center of the fan clutch.